Witch Doctor was my first class, completed Act 1, then I raised my Monk. He's currently up to the Moon Clan den after clearing the Cathedral.
Gonna start working on a Sorceror/Wizard/<w/e its called> next, and keep them all at around the same level (I'm going to make sure they all get to like Act 2 before I start Act 3, etc.).

By Blizzard Entertainment:
Part of the reason is that Battlegrounds are like ducks.

I was really expecting 1 class to dominate the others, it's been pretty balanced though so far! I'm a monk, fucking LOVE it. So many cool abilities, love the Russian accent, and he looks like Rasputin from Hellboy.